var isMergeableObject = (function () {
    return function isMergeableObject(value) {
        return isNonNullObject(value)
            && !isSpecial(value)
    }
    
    function isNonNullObject(value) {
        return !!value && typeof value === 'object'
    }
    
    function isSpecial(value) {
        var stringValue = Object.prototype.toString.call(value)
    
        return stringValue === '[object RegExp]'
            || stringValue === '[object Date]'
            || isReactElement(value)
    }
    
    var canUseSymbol = false;
    var REACT_ELEMENT_TYPE = 0xeac7;
    try {
        // canUseSymbol = typeof Symbol === 'function' && Symbol.for
        // if (canUseSymbol) {
        //     REACT_ELEMENT_TYPE = canUseSymbol ? Symbol.for('react.element') : 0xeac7;
        // }
    } catch(e) {
    
    }
    
    
    function isReactElement(value) {
        return value.$$typeof === REACT_ELEMENT_TYPE
    }
})()

function emptyTarget(val) {
	return Array.isArray(val) ? [] : {}
}

function cloneUnlessOtherwiseSpecified(value, optionsArgument) {
	var clone = !optionsArgument || optionsArgument.clone !== false

	return (clone && isMergeableObject(value))
		? deepmerge(emptyTarget(value), value, optionsArgument)
		: value
}

function defaultArrayMerge(target, source, optionsArgument) {
	return target.concat(source).map(function(element) {
		return cloneUnlessOtherwiseSpecified(element, optionsArgument)
	})
}

function mergeObject(target, source, optionsArgument) {
	var destination = {}
	if (isMergeableObject(target)) {
		Object.keys(target).forEach(function(key) {
			destination[key] = cloneUnlessOtherwiseSpecified(target[key], optionsArgument)
		})
	}
	Object.keys(source).forEach(function(key) {
		if (!isMergeableObject(source[key]) || !target[key]) {
			destination[key] = cloneUnlessOtherwiseSpecified(source[key], optionsArgument)
		} else {
			destination[key] = deepmerge(target[key], source[key], optionsArgument)
		}
	})
	return destination
}

function deepmerge(target, source, optionsArgument) {
	var sourceIsArray = Array.isArray(source)
	var targetIsArray = Array.isArray(target)
	var options = optionsArgument || { arrayMerge: defaultArrayMerge }
	var sourceAndTargetTypesMatch = sourceIsArray === targetIsArray

	if (!sourceAndTargetTypesMatch) {
		return cloneUnlessOtherwiseSpecified(source, optionsArgument)
	} else if (sourceIsArray) {
		var arrayMerge = options.arrayMerge || defaultArrayMerge
		return arrayMerge(target, source, optionsArgument)
	} else {
		return mergeObject(target, source, optionsArgument)
	}
}

deepmerge.all = function deepmergeAll(array, optionsArgument) {
	if (!Array.isArray(array)) {
		throw new Error('first argument should be an array')
	}

	return array.reduce(function(prev, next) {
		return deepmerge(prev, next, optionsArgument)
	}, {})
}

module.exports = deepmerge